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Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. [1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. [2]
The liquid and solid exchanges that take place in the microvasculature particularly involve capillaries and post-capillary venules and collecting venules. [citation needed] Capillary walls allow the free flow of almost every substance in plasma. [6] The plasma proteins are the only exception, as they are too big to pass through. [5]
The venous system apart from the post-capillary venules is a high volume, low pressure system. Vascular smooth muscle cells control the size of the vein lumens, and thereby help to regulate blood pressure. [31] The post-capillary venules are exchange vessels whose ultra-thin walls allow the ready diffusion of molecules from the capillaries. [10]
The walls of the dural venous sinuses are composed of dura mater lined with endothelium, a specialized layer of flattened cells found in blood and lymph vessels.They differ from other blood vessels in that they lack a full set of vessel layers (e.g. tunica media) characteristic of arteries and veins.
They are part of the circle of Willis, which provides backup circulation to the brain. In case one of the supply arteries is occluded, the circle of Willis provides interconnections between the anterior and the posterior cerebral circulation along the floor of the cerebral vault, providing blood to tissues that would otherwise become ischemic .
Major gyri and sulci on the lateral surface of the cortex Lobes of the brain. The cerebrum is the largest part of the brain and is divided into nearly symmetrical left and right hemispheres by a deep groove, the longitudinal fissure. [17] Asymmetry between the lobes is noted as a petalia. [18]
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Most famous parts of the brain highlighted in different colours. The human brain anatomical regions are ordered following standard neuroanatomy hierarchies. Functional, connective, and developmental regions are listed in parentheses where appropriate.